Aqueous dispersion of a copolymer of methylmethacrylate and beta-hydroxyethylmethacrylate



United States Patent 6-" AQUEOUS DISPERSION OF A COPOLYMER FMETHYLMETHACRYLATE A N D BETA HY- DROXYETHYLMETHACRYLATE 'Jizeng JiueqSuen, New Canaan, and William C. Meisenhelder, Darien, Conn., assignorsto American Cyanamid Company, Stamford, Conn., a corporation of Maine NoDrawing. Filed Mar. 24, 1965, Ser. No. 442,516

1 Claim. (Cl. 26029.6)

This application is a continuation-in-part of application Serial No.198,439, filed May 29, 1962, now a'bandoned.

This invention concerns certain novel aqueous dispersions useful in thepreparation of translucent films. More specifically, the presentinvention deals with the manufacture of a novel cross-linkable copolymercontaining aqueous dispersion or latice, which when coated on asubstrate, dried and heat-treated is capable of providing a glossy,continuous, substantially insoluble and infusible film of excellenthardness, strength, chemical resistance and clarity.

Film-forming copolymer-containing aqueous dispersions, especially thosewherein the copolymer has been prepared by emulsion copolymerization ofacrylic monomers, are Well known in the 'art and have been employed in avariety of coating applications. Normally, the monomers used inpreparing such emulsion copolymers are of two distinct typeshardeningmonomers, i.e., those Whose glass transition temperatures are about 3035 C. and which tend to form relatively inflexible polymers; andsoftening monomers, i.e., those whose glass transition temperatures arebelow about 20 C. and which tend to form soft, flexible polymers.Unfortunately, experience with dispersions of emulsion copolymerscontaining preponderant amounts of either hardening or softeningmonomers have for the most part proven unsatisfactory where themanufacture of films is concerned. For example, in those instances wherehardening monomers are used in major amounts, resulting polymers, unlessplasticized, will not form films at room temperature or higher by simpledeposition on .a substrate. Moreover, the situation is not alleviated byadding a conventional non-reactive plasticiz/er such as dibutylphthalate, because the volatilization of the plasticizer whether duringor after the formation of the film can lead to detrimental changes inthe physical properties of the film such as shrinkage, embrittlement,etc. In those cases where the plasticizers remain in the film afterformation, they tend to cause various undesirable properties in thefilm, such as diminished solvent resistance, lack of clarity, andsoftening of the material. On the other hand, films formed from emulsioncopolymers containing a preponderant moiety of softening monomers sufferfrom the deficiency of lack of hardness, durability and chemicalresistance essential to most coating or laminate applications.

According to the concept of the present invention, We have nowdiscovered that a particular class of highly alkoxymethylate melamineswill not only function as a plasticizing agent in the formation offilm-forming emulsion copolymers containing quantities of hardeningmonomers, but also serve to cross-link continuous films prepared fromcopolymers of this class containing co- Patented Nov. 8, 1966 monomershaving functional groups reactive with an N- hydroxymethyl or-alkoxymethyl function to form substantially insoluble and infusiblefilms. This concept, to the best of our information and belief, hasnever before been appreciated; and it becomes an object of our inventionto provide a novel aqueous dispersion which corresponds to theattributes of the aforesaid material.

A further object of our invention is to provide the art with a novelaqueous dispersion capable of forming continuous films and whichcomprises reactive aqueous emulsion copolymers containing sufficientquantities of hardening c'omonomers that they will not form films atambient temperatures after simple deposition on a substrate, thuspermitting the use of such copolymers in preparing continuous films.Further, our invention relates to the use with the aforesaid material ofrelatively large quantities of highly alkoxymethylated melamine resinsas plasticizing and cross-linking agents. These and other objects of ourinvention will be more elaborately exemplified by recourse to thefollowing description as well as the several specific embodiments of ourinvention presented.

Briefly stated, the novel aqueous dispersion of our invention comprisestwo essential components. The first component is a reactivewater-insoluble emulsion copolymer prepared from about 50 to about 98%by weight, and preferably from about to about by weight, based on thetotal weight of monomers in the copolymer, of (A) a monoethylenicallyunsaturated hardening comonomer containing no functional groups capableof reaction with an N-hydroxymethyl or N- alkoxymethyl group, forexample, methylmethacrylate; and from about broadly 220% by weight, butpreferably from about 510% by weight of (B) a monoethylenicallyunsaturated comonomer containing a functional group which is reactivewith an N-hydroxymethyl or N- alkoxymethyl group. An example of thiscomonomer would be acrylic acid or methylacrylic acid.

While as stated above the preferred comonomer (A) is methylmethacrylate,certain other alkyl methacrylates such as ethylmethacrylate,propylmethacrylate, n-butylmethacrylate, isobutylmethacrylate, and thelike, as well as mixtures thereof may also be employed in addition to orinstead of methylmethacrylate. Comonomer (B), on the other hand, ispreferably an acrylic acid, an acrylic acid amide, or a hydroxylatedalkyl ester of an acrylic acid, and is preferably itself a hardeningcomonomer. Included among the reactive group containing monomers arethose such as ethacrylic acid, oc-ChlOIOEIClYllC acid, the correspondingamides, e.g., acrylamide, methacrylamide and the like, as well as thehydroxylated alkyl esters of acrylic and methacrylic acid such as,B-hydroxyethyl methacrylate, ,B-hydroxyethyl acrylate, fi-hydroxyethyloU-ohloroacrylate, -hydroxypropylacrylate, B-hydroxy- 'butylmethacrylate, and the like.

If desired, the reactive water-insoluble emulsion copolymer may alsoinclude (C) a monoethylenically unsatumethyl acrylate, ethyl acrylate,propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, octylacrylate, dodecyl acrylate, and the like, as well as mixtures thereof,and can be present in the copolymer in amounts ranging from to about 45%by weight, based on the total weight of monomers in the copolymer,depending on the properties or combinations of properties, e.g.,hardness coupled with flexibility, desired in the final product.Comonomer (C), if employed, will generally replace part of comonomer(A), but in any event, the total amount of hardening monomer(s) presentwill be such that the copolymer, if unplasticized, will be incapable offorming continuous films at ambient temperatures. This usually meansthat the copolymer will contain not less than about 50% by weight, basedon the total weight of monomers in the copolymer, of hardeningmonomer(s). Furthermore, in every case the total amount of comonomers(A), (B) and (C) employed will equal 100%.

Suitable methods for the preparation of aqueous emulsion copolymers ofthe type employed in practicing the present invention from monomers suchas those listed hereinabove are so numerous and so well known in the artthat only the most cursory treatment is necessary here. In general, theselected comonomersare emulsified in water, using from about 1% to aboutby weight, based on the total weight of monomers present, of aconventional emulsifying agent. This emulsifying agent can be non-ionic,e.g., an alkylphenoxypolyethoxyethanol having alkyl groups of from about7 to about 18 carbon atoms in length and from about 6 to about 60oxyethylene units, such as the heptylphenoxypolyethoxyethanols,met-hyloctylphenoxypolyethoxyethanols, dodexylphenoxypolyethoxyethanols,and the like; a long chain fatty acid derivative of sorbitol, such assorbitan monolaurate, monopalmitate, monostearate, tristearate, and thelike; an ethylene oxide derivative of an etherified or esterifiedpolyhydroxy compound having a hydrophobic carbon chain, such aspolyoxyethylene sorbitan monolaurate, monopalmitate, monostearate, andthe like, anionic, e.g., sodium lauryl sulfonate, sodiumisopropylnaphthalene sulfonate, diisobutyl sodium sulfosuccinate,di-Z-ethylhexyl sodium sulfosuccinate, and the like, or a mixture ofnon-ionic and anionic emulsifying agents. Since the pH of the aqueousdispersion of the emulsion copolymer will be adjusted to at least 7, andpreferably higher, prior to adding the highly alkoxymethylated melamine,cationic emulsifying agents, due to their instability under basicconditions, are not particularly preferred.

The emulsified comonomers are copolymerized by means of a catalyticamount of a conventional free radical polymerization catalyst orcatalyst system, e.g., an inorganic or organic peroxide such as hydrogeneroxide, tbutyl hydroperoxide, cumene hydroperoxide, and the like, anazo nitrile, such as u,a'-azobisisobutyronitrile and the like, aninorganic persulfate, such as ammonium persulfate, sodium persulfate,potassium persulfate, and the like, or a redox catalyst system, such assodium metabisulfitepotassium persulfate and the like. The particularcatalyst or catalyst system chosen can generally be used in amountsranging from about 0.01% to about 3% by weight, based on the totalweight of comonomers present. The polymerization reaction can be carriedout at temperatures ranging from about 0 C. to about 100 0., preferablyat from about room temperature (25 C.) to about 70 C., and the emulsionwill preferably be agitated during the reaction. The resulting aqueousemulsion copolymer can have a molecular weight ranging from about 25,000to about 1,000,000 or higher, as determined by intrinsic viscositymeasurements [see Flory, Principles of Polymer Chemistory (Ithaca, N.Y.,Cornell University Press, 1953) pages 308 to 311], and will generally bepresent in the dispersion in amounts ranging from about 30% to about 60%by weight, and usually from about 40% to about 50% by weight, based onthe total weight of the dispersion at this point.

' slightly lower degree of methylolation or alkylation.

As previously indicated, following the copolymerization reaction the pHof the aqueous dispersion is adjusted to at least 7, e.g., to between 7and about 10, and preferably to between about 7.5 and about 9.5. This isdone in order to maintain a stable system once the highlyalkoxymethlated malamine is added to the dispersion. Any basicsubstance, e.g., sodium hydroxide, potassium hydroxide, and the like,may be used to adjust the pH, but it is preferred that the basicsubstance employed by a volatile base, such as ammonia, triethylamine,and the like, which can be volatilized off to provide the acidicconditions necessary for the highly alkoxymethylated melamine tocross-link the thermosetting aqueous emulsion copolymer through itsreactive functional groups.

The second essential component of our novel aqueous dispersions is ahighly alkoxymethylated melamine represented by the general formula:

MF A

wherein M represents melamine, the starting material, F represents thedegree to which the melamine starting material has been methylolated,with x representing a number between about 5 and 6, inclusive, and Arepresents the degree to which the methylol groups of thepolymethylomelamine intermediate have been alkylated with lower alkylgroups containing from 1 to 3 carbon atoms, inclusive, i.e., methyl,ethyl and propyl groups, to provide alkoxymethyl groups containing from2 to 4 carbon atoms, inclusive, in the highly alkoxymethylated melaminefinal product, with y representing a number between 5 and 6, inclusive.Thus, the highly alkoxymethylated melamines employed in the practice ofthe present invention include the hexa-alkyl ethers ofhexamethylolmelamine, such as hexakis(methoxymethyl)melamine and thelike, which represent the highest degree of methylolation and alkylationobtainable, the penta-alkyl ethers of hexamethylolmelamine, such as thepentamethyl ether of hexamethylolmelamine and the like, and thepenta-alkyl ethers of pentamethylolmelamine and the like. Furthermore,as is evident from the general formula and the values of x and y givenabove, one can use mixtures of these highly alkoxymethylated melamines,e.g., a mixture of hexakis (methoxymethyl)me1amine and the pentamethylether of hexamethylolmelamine, as well as mixtures containing minoramounts of alkoxymethylated melamines having a In such cases x and yrepresent average values for the degree of methylolation and alkylation.Hexakis (methoxymethyl)melamine or mixtures containing a major amountthereof together with minor amounts of other highly methoxymethylatedmelamines having slightly lower degrees of methylolation and methylationare preferred for use in practicing the present invention.

Highly alkoxymethylated melamines are prepared by methods which are sowell known in the art that it is not necessary that they be set forthherein in any great detail. In general, these conventional methodsinvolve the basic steps of reacting melamine with aqueous formaldehydein mol ratios ranging from about 6.5 to about 20 mols or more offormaldehyde per mol of melamine to form polymethylolmelamines; removingthe bulk of the water from the thus-formed polymethylolmelamines, andthereafter reacting the polymethylolmelamines, under acidic conditions,with from about 10 to about 20 mols of a lower alkanol, such asmethanol, ethanol, propanol, and the like, per mol of melamine startingmaterial. Various modifications and improvements of this basic processhave been developed, such as those set forth in Us. Patents Nos.2,715,619 to Suen et al. and 2,918,452 to Kun et al.

The highly alkoxymethylated melamine can be added to the aqueousdispersion containing the thermosetting copolymer either as a liquidmelt or as a high solids dispersion in water, e.g., a dispersion ofhighly alkoxymeth- 5. ylated melamine containing from about 30% to about60% solids, and preferably from about 40% to about 50% solids. Theplasticizing amount of highly alkoxymethylated melamine employed canrange from about to about 100% by weight, based on the weight of thereactive copolymer, depending on the composition of the particularreactive copolymer employed, the highly alkoxymethylated melamine ormixture of highly alkoxymethylated melamines used to plasticize thecopolymer, and the temperature at which the aqueous dispersioncontaining these two essential ingredients is dried.

While we do not wish to be bound by any particular theory or reactionmechanism advanced to explain the operation of the invention, it isbelieved, as previously indicated, that the highly alkoxymethylatedmelamine component of our novel aqueous dispersions performs a twofoldfunction therein. First of all, it acts to plasticize the acryliccopolymer component, which is still in the thermoplastic state,coalescing the separate reactive copolymerparticles during the time atwhich the dispersion or latex, cast on a suitable substrate, is beingdried, thereby providing a continuous film. As stated hereinabove, thetemperature at which our novel aqueous dispersions can be dried rangesfrom a maximum of about 170 C. to a minimum of about 25 C. or, in otherwords, to about room temperature, and at these temperatures drying willusually take about minutes or more. In addition to its plasticizingfunction, the highly alkoxymethylated melamine also serves to efiectcross-linking between the essentially linear reactive acrylic copolymerchains by reacting with the residual functional groups, i.e., thecarboxyl, amide or hydroxyl groups, contained therein. This crosslinking reaction is carried out at temperatures ranging from about 100C. to about 200 C. for periods of time ranging from about 2 minutes toabout 60 minutes. From this, it can be seen that the cross-linkingreaction can take place either during the drying step, if drying iscarried out at sufiiciently elevated temperatures, or subsequentthereto, if drying is carried out at relatively low temperatures, e.g.,at room temperature.

The unexpected and visibly apparent advantage characterized by thecomposition of our invention over those previously known to the art maybe summarized by stating that prior to our filing it had not beenpossible to use polymers with high amounts of hardening monomer withoutthe use of a volatile plasticizer or elevated temperatures for dryingthe emulsion and obtain a continuous film. This we have achieved by theaddition of hexakis (methoxymethyl)melamine plasticiZer-cross-linkingagent. As can be seen, the use of our system permits the practical,everyday use of an aqueous dispersion of comonomers with the resultantdisregard for molecular weight which in a one-phase system would poseimmediate problems of viscosity. Thus, with our unique approach, we arenot only able to have a desirable two-phase system, but we are able todo so with an added advantage to being able to transform this aqueousemulsion into a clear, homogeneous molded film. Moreover, all of thiscan be done without the need for massive amounts of expensive anddangerous organic solvents. This is the nub of our invention, and it isbelieved to be unique in this regard.

In those cases where a non-volatile base is employed to adjust the pH ofthe-system to the basic side prior to the addition of the highlyalkoxymethylate melamine or where it is desired to accelerate thecross-linking reaction, from about 0.1% to about 1% by weight, based onthe combined weights of the thermosetting acrylic copolymer and thehighly alkoxymethylate melamine, of a conventional acidic curingcatalyst, such as paratoluenesulfonic acid, benzenesulfonic acid,hydrochloric acid or other acid salts of tertiary amines, such astriethylamine, or hydroxyalkyl amines, such as2-methyl-2-amino-l-propanol, and the like, can be added to the aqueousdispersion prior to drying. Similarly, other conventionally employedadditives, such as pigments, dyes, fillers, powdered or flaked 6.metals, ultraviolet light absorbers, and the like, can also be added atthis point.

As previously mentioned, our novel aqueous dispersions are particularlyuseful as coating compositions, and may be used to coat varioussubstrates such as metals, wood, glass, asbestos cement siding, and thelike to provide protective as well as decorative qualities, especiallywhere such materials are to be used for outdoor applications, e.g., asexterior surfacing members for houses and the like.

In order that those skilled in the art may more fully understand theinventive concept presented herein, the following illustrative examplesare set forth. These examples are given solely by way of illustrationand should not be considered as expressing limitations unless so setforth in the appended claims. All parts and percentages are by weight,unless otherwise stated.

PREPARATION OF DISPERSION A.70/20/ 10 METHYLMETHACRYLATE ETHYLACRYL-ATE/METHACRYLIC ACID A solution containing 8 parts of dioctyl sodiumsulfosuccinate and 0.26 part of sodium bicarbonate dissolved in 600parts of water was charged to a suitable reaction vessel equipped withthermometer, stirrer and inert gas inlet tube. After flushing thesolution with nitrogen gas (a stream of nitrogen gas was employed tomaintain an inert atmosphere throughout the reaction) and then heatingit to 60 C. with stirring (stirring being continued throughout thepreparation), 0.44 part of ammonium persulfate was added, followed twominutes later by 40 parts of a monomer solution consisting of 280 partsof methyl methacrylate, parts of ethyl acrylate and 40 parts ofmethacrylic acid. The temperature of the resulting emulsion was allowedto rise to 80 C. and was then maintained at between 80 C. and 90 C. forthe remainder of the reaction. The balance of the monomer solution wasthen added to the emulsion over a period of one hour. After the lastaddition of the monomer solution the emulsion was heated for anadditional hour and then cooled to room temperature. Finally, thepolymer dispersion, which had a solids content of 40.4%, was adjusted toa pH of 7.0 with amonium hydroxide.

PREPARATION OF DISPERSION B.-90/l0 METH- YLMETHACRYLATE/METHACRYLICACID.

A solution containing 4.5 parts of dioctyl sodium sulfosuccinate and 0.3part of sodium bicarbonate dissolved in 537 parts of water was chargedto a suitable reaction vessel equipped with thermometer, stirrer andinert gas inlet tube. After flushing the solution with nitrogen gas (astream of nitrogen gas was employed to maintain an inert atmospherethroughout the reaction) and then heating it to 60 C. with stirring(stirring being maintained throughout the preparation), 28 parts of asolution of 0.5 part of ammonium persulfate in 35 parts of water wereadded, followed five minutes later by 116 parts of a monomer-emulsifiersolution consisting of 405 parts of methyl methacrylate, 45 parts ofmethacrylic acid and 13 parts of Triton X-305 (a 70% active solution ofan octylphenol-ethylene oxide condensate). The temperature of theresulting emulsion was allowed to rise to C. and the remainder of themonomer-emulsifier solution was added dropwise to the emulsion over aperiod of one hour, during which time the temperature was maintainedbetween 75 C. and 91 C. After the last addition of themonomer-emulsifier solution the remainder of the abovedescribed ammoniumpersulfate solution Was added to the emulsion and the temperature washeld at 91 C. for an additional 5 minutes. The polymer dispersion wasthen cooled to 30 C. and adjusted to a pH of 8.2 with concentratedammonia. It had a solids content of 45.7%.

PREPARATION OF DISPERSIONS C-O In a manner similar to that described forthe prepara tion of dispersions A and B, the aqueous dispersionsdescribed in Table I below in terms of their polymeric components, pHsand solids concentrations were prepared.

Example 1 One hundred parts of Dispersion A were admixed with TABLE I 39parts of a 35% aqueous dispersion of hexak1s(me- Percentthoxymethyl)rnelamine. A 12-m1l (wet thickness film of DispersionPolymeric Component pH Solid this mixture was then deposited on a glassplate and air-dried at room temperature (approximately 25 C.) to give aclear, contlnuous film. The dried film was then gg/agL n r w i nm 1.7baked at 165-170 C. for 30 minutes to give a hard,

1 l {I I I 7,5 35 clear, colorless, continuous film, insoluble inacetone.

7.0 35 7.6 41 7.6 39 7 8 41 Example 2 7.7 42 80/10/10MMA/EA/l\lAA 7.5 43The procedure of Example 1 was repeated using Dis- 50/45/5MMA/EA/MAA 7.9 46 47/45/8MMA/EA/MAA 7. 8 4o. 6 perison A without any hexakis(methoxymethyhmelamine.

:1 When air-dried at room temperature this unmodified d'lSPCISlOI'l didnot give a cont-muons film, and even after o 1 Monomers are expressed inparts, e.g., Dispersion 0 contains a 00- bakmg for 30 mlmltes at 165-170the fi m remained polymer of 60 parts of methylmethacrylate, 35 parts ofethyl aerylate and soluble in acetone 5 parts of methaerylic acid.

MMA=n1ethylmethaerylate. BMA=butylmetl1aerylate. ExamplesEA=ethylacrylate.

:0. Y 1 fifii gfgfiggg The procedure of Example 1 was repeated in eachcase S=styrene with the modifications noted in Table II below. Thel\iAA=methaeryl1eae1d. AA=aerylie acid. characteristics of the filmsobtained are also listed in fl-HEMA=fi hydroxyethylmethaerylate. TableII MA =1nethaeryla1nide.

TABLE II Hexakis(meth- I Example Dispersion Amount oxymethyl) AnlountDrying Condltions Baked F l melamine 3 B 100 35% aqueous 39 Air-dried atroom temperature for Hard, clear, colorless, continuou dispersion.minutes, then baked at 165-170 C. for

30 minutes. 100 do Non-continuous.

50 50% aqueous 7.9 do H r lear, colorless, tou h, commdispersion, nous,good adhesion to glass. 50 d PencrlHardness=HB-F. 0 N on-eontinuous. 100aqueous Hard, clear, colorless, continuous.

dispersion. 9 D 100 aqueous 21 Air-dried at room temperature for Hard,clear, continuous, good gloss, dispersion. minutes, then baked at 170 C.for

30minutes. 1 D do 28 O- 11 D 100 do Non-continuous. 12 E 100 35% aqueous39 Air-dried at room temperature for 30 Hard, clear, continuous.

dispersion. minutes, then baked at 170 C. for 30 minutes. 1? E 100 50%aqueous 35 Air-dried at room temperature for 20 Do.

dispersion. minutes, then baked at 170 O. for

30 minutes. 100 Air-dried at room temperature for 30 Non-continuous.

minutes, then baked at 170 C. for 30 minutes. 100 50% aqueous 21Air-dried at room temperature [or 15-20 Hard, clear, continuous.

dispersion. minutes, then baked at 170 C. for

30 minutes. 100 do 28 do Do. 100 do Non-continuous. 100 50% aqueous 23.8Air-dried at room temperature for 15 Clear, colorless, tough,continuous, dispersion. minutes, then baked at C. for excellent adhesionto glass.

30 minutes. Peneil Hardness: 19 G 100 d0 29.8 .d0 20 G 100 do 39.7 do19=FH. 20=FH. 21 G 100 Non-continuous. 22 H 50 50% aqueous 7.5 Air-driedat room temperature [or 25 Hard, clear, continuous, good adh siodispersion. minutes, then baked at -170 C. to glass.

for 30 minutes. Pencil Hardness: 23 H 50 .d0 11.2 do 22= 50 do 15 do23=FH.

24=HBF. 50 .do Non-continuous. 100 50% aqueous 14 Air-dried at roomtemperature, then I-lard, clear, continuous.

dispersion. baked at 165-170 C. for 30 minutes. 100 ..do Non-continuous.

50 50% aqueous 30 Air-dried at room temperature for 10 Hard, clear,continuous.

dispersion. hours, then baked at C. for 30 minutes. do Do. do Do. Bakedat 150 C. for 30 minutes Do. Ailr-dried at room temperature for 16Non-continuous.

ours. Baked at 150 C. for 30 minutes Do.

'-Fi1m thickness (wet) was 9 mils.

Example 34 A white enamel was formulated by first grinding the followingcomponents in a ball mill for 2 hours to give a pigment grind.

Component: Parts Titanium dioxide 1 200 Tamol 731 2 8 Triton CF-lO 3 4Nopco 1497-V 2 Cellosize QP-4400 25 1 Pigment.

2 Dispersing agent; a sodium salt of a polymeric oarboxylio acitl.'

Wetting agent; an alkyl aryl polyether alcohol.

4 A lanolin-type autifoaming agent.

5 Thickener; hydroxyethyl cellulose.

Next, 64 parts of hexakis(methoxymethyl)melamine were melted and addedto 490 part-s of Dispersion A, from which sufiicient water had beenremoved to adjust the solids content to 46%. The pigment grind was thenadded to the plasticized dispersion and homogeneously blended therewithto give an enamel having a total solids content of 47% and a vehiclesolids content of 32.5%. A 3-mil (wet thickness) film of this enamel wasthen cast on a -inch thick cold rolled steel panel and baked for 30minutes at 149 C., following which the baked film was allowed to cool toroom temperature and then tested for its impact strength (by the fallingball test carried out on the front, or enameled, side of the panel) andpencil hardness. The results of these tests are summarized in Table IVbelow.

Examples 35-42 The procedure of Example 34 was repeated in every detailbut one, namely, Dispersion A was replaced with equal amounts ofDispersions C, H, I, M, N, and 0 respectively (in each case the solidscontent of the dispersion employed was adjusted to 46%). The results ofthe tests made on the enamel films of these examples are also given inTable IV.

TABLE IV Impact Pencil Dispersion Strength 1 Hardness 20 311-411 3011-211 26-36 11-211 16-18 3II-4H 70 H-2H 36 2H -3H 36 2H3H 1 Ininch-pounds.

1o Example 43 Hexakis(methoxymethyl)melamine andtetrakis(methoxymethyl)benzoguanamine were admixed with separate samplesof Dispersion M in amounts sufficient to give 33% plasticizer, based onthe weight of the copolymer in the dispersion (23% plasticizer whenbased on total solids, i.e., plasticizer and copolymer), in each sample.A 3-m=il (wet thickness) fihn was then deposited from each plast-icizedsample onto a glass plate and allowed to airdry at room temperature. Thedried film plasticized with hexakis(methoxymethyl)melamine wascontinuous, whereas the film plasticized with tetrakis (methoxymethyl)benzoguanamine was non-continuous.

Example 44 Hexakis (methoxymethyl)melamine anddimethoxymethylmonome-thylolmelamine were admixed with separate samplesof Dispersion A in amounts sufiicient to give 30% plasticizer, based onthe weight of the copolymer in the dispersion, in each sample. A 3-mil(wet thickness) film was then cast from each plasticized sample onto aglass plate and allowed to air-dry for 20 minutes at room temperature.The dried film plasticized with hexakis(methoxymethyl)melamine was clearand continuous, whereas the film plasticized withdimethoxymethylmonomethylolmelamine was non-continuous.

Each film was then baked for 35 minutes at 165 C. Thehexakis(methoxymethyl)melamine-plasticized filrn was hard, clear andcontinuous after this heat-treatment. Thedimethoxymethylmonomethylolmelamine-plasticized film, althoughcontinuous in the center, showed many fine cracks throughout the rest ofthe film. In addition, its outer edge was powdery.

It will be obvious to those skilled in the art that other changes andvariations may be made in carrying out the present invention withoutdeparting from the spirit and scope thereof as defined in the appendedclaim.

We claim:

A composition comprising an aqueous dispersion capable of formingsubstantially insoluble and infusible continuous films comprising:

(1) a reactive water-insoluble emulsion copolymer of (A) from about toby weight of methylmethacrylate and (B) from 2 to 20% by weight ofBahydroxyethylmethacrylate, and (2) a plasticizing quantity of hexakis(methoxymethyl) melamine.

References Cited by the Examiner UNITED STATES PATENTS 2,906,724 9/1959Daniel 260856 2,994,676 8/1961 Kucsan et a1 260-29.6 3,107,227 10/1963Suen et al. 260 -853 OTHER REFERENCES Principles of Polymer Chemistry,Flory, Cornell University Press, Ithaca, New York, 1953, pages 203-4.

MURRAY TILLMAN, Primary Examiner. P. LIEBERMAN, Assistant Examiner.

